The invention relates generally to systems for protecting spacecraft from charging, and more specifically it relates to a new kind of system for the mitigation of spacecraft surface charging using ionized water vapor. The use of ionized water vapor has many advantages over other methods: much lower cost, efficient electron scavenger, efficient evaporation rate helps taking excess surface electrons away, leaving practically no residue after complete evaporation.
Charging of spacecraft in the energetic plasma environment in space may be hazardous to the health of on-board electronics. It may affect telemetry, navigation, operation and even the survivability of spacecraft, and degrade scientific measurements. Spacecraft charging may be due to natural or artificial causes. Natural charging is due to the interaction between a spacecraft and its space plasma environment. Artificial charging is due to beam emissions, for example. In the geosynchronous environment, a spacecraft is often charged negatively during eclipse.
The task of providing spacecraft radiation protection using technology is alleviated by the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 5,594,325 issued to David Manner
U.S. Pat. No. 4,691,159 issued to Ahrens et al.
U.S. Pat. No. 4,899,269 issued to Rouzies
U.S. Pat. No. 5,394,075 issued to Ahrens et al.
U.S. Pat. No. 5,444,358 issued to Delepaunt
U.S. Pat. No. 5,451,858 issued to Van Duyne et al.
The above-cited references describe patented space radiation protection systems. The Manner patent describes the use of spacecraft power systems to mitigate spacecraft charging effects.
Geosynchronous spacecraft have a history of charging anomalies. Conventional passive protection measures are often complex and costly.
The present invention is a system for mitigating spacecraft charging by means of ionized water vapor. More specifically, when water vapor molecules are evaporating from charged spacecraft surfaces, the evaporation carries away the excess surface electrons.
Water molecules are effective charge scavengers. In the low atmospheric pressure (practically a vacuum) space environment, neutral and charged water droplets on the spacecraft surface evaporate rapidly, especially on the sunlit surface of the spacecraft. When the evaporating charged droplet radius diminishes to a critical rayleigh size, the droplet would burst into several smaller droplets and electrons are carried away by the smaller droplets.
In the present invention, we use ionized water vapor for mitigation, the water vapor comes out from a heated tray through a very fine mesh instead of from a single nozzle. The mesh holes are of hundredth of a cm. in diameter or smaller. This method prevents the condensation of an expanding water jet into ice particles of substantial sizes. In addition, we use an ionization device to generate positively ionized water vapor. The water vapor ions return to the negatively charged spacecraft and neutralize the excess negative surface charge while the ionization electrons leave the spacecraft and carry away negative charges.